As a conventional rain gauge, generally a rain gauge with a tipping bucket has been widely used. FIG. 1 is a drawing for illustrating an overview of such the rain gauge with a tipping bucket.
The rain gauge with a tipping bucket is configured to have a conical funnel 1A as a catchment unit for catching the dropping rainwater, and a tipping bucket 1B which reserves a certain amount of the rainwater caught by conical funnel 1A and tips over to any direction around a pivot point.
The tipping bucket 1(B) includes catchment bucket units I and II respectively on the left and the right sides, each of which has the same specified capacity. When the catchment bucket unit I on one side reserves a specified amount of rainwater (FIG. 1(A)), the catchment bucket unit I tips over by its weight around the pivot point and drains off the reserved rainwater. Then, the tipping bucket unit II on the other side starts to reserve the rainwater (FIG. 1(B)). Further, when the specified amount of the rainwater is reserved in the other catchment bucket unit II, again the catchment bucket unit II tips over and drains off the reserved rainwater, then the condition transits to as illustrated in FIG. 1(A).
Then, every time the tipping bucket 1B tips over, a switch not illustrated is turned on. Thus, from the number of times of the switch being turned on in a specified period and the specified capacity of the catchment bucket units I and II, the total rainfall amount or the rainfall amount per unit time can be obtained.
Here, the conventional rain gauge with a tipping bucket illustrated in FIG. 1 is configured to catch the dropping rainwater by the conical funnel 1A. Therefore, in FIG. 2 for explaining problems of the rain gauge with a tipping bucket, when the rainwater drops in the perpendicular direction under a windless condition (FIG. 2(A)), rainfall amount can be measured accurately.
However, as illustrated in FIG. 2(B), when the rainwater drops in the inclined direction under a windy condition, the cylindrical outer shape causes inconsistency of the surrounding wind and the amount of the rainwater which cannot be caught by the catchment surface at the top of the cylinder increases. In such a case, an accurate measurement of the rainfall amount becomes difficult.
For example, on a steep inclined land, the rainwater comes flying in the horizontal direction by a wind blowing up, theretofore, an accurate measurement of the rainfall amount by the conventional rain gauge with a tipping bucket as illustrated in FIG. 1 is difficult.
To address such problem, improvements on the catchment unit have been proposed (examples are illustrated in Patent documents 1 and 2).
An invention described in Patent document 1, relates to a rain gauge with a tipping bucket having a spherical catchment unit (or water gathering unit), for the place of the funnel 1 of the rain gauge with a tipping bucket. That is, the invention of patent document 1 has such configuration as to gather the rainwater caught by the spherical catchment unit having a circular catchment plane which can be projected as a certain circular area to all azimuth and zenith directions.
An invention described in Patent document 2 has a semispherical catchment unit, instead.
Patent Document 1: Japanese Laid-Open Patent Publication 2006-17462
Patent Document 2: Japanese Laid-Open Patent Publication 2003-21689